This invention relates to novel photosensitive sheet construction which, when exposed to a suitable light energy source through a screened image, will yield simultaneously both a negative and positive reproduction of said screened image.
The novel photosensitive sheet construction of this invention are particularly useful in the graphic arts field. For example, in the lithographic printing arts, it is frequently necessary or desirable to convert a negative film image to a positive one for further use in the preparation of lithographic printing plates. Heretofore, this conversion from a negative to positive image, and vice versa, has been time consuming, expensive and inefficient. We have now discovered a novel imaging system and product which can directly, efficiently and inexpensively be employed to convert a negative image to a positive one, and vice versa.
The novel imaging system and products of this invention comprise a layered or sandwich type sheet construction, which in one embodiment is comprised of the following elements:
1. A top sheet; PA1 2. A light sensitive gas generating diazonium layer applied to and contacting at least one surface of said top sheet; PA1 3. An imaging layer which is applied to and in contact with the surface of said diazo layer; PA1 4. An adhesive layer which is in contact with the surface of said imaging layer; and PA1 5. A base sheet layer supporting said adhesive layer and bound thereby to said other layers.
Said image layer and/or said adhesive layer comprise light sensitive photohardenable or photocrosslinkable materials.
In another embodiment said adhesive layer and said imaging layer may be combined to form a single stratum and in still other embodiments the base sheet layer may be completely eliminated from both of the previously mentioned constructions. These arrangements will be more completely described hereinafter.
To date, it has been a problem in the art to provide an imaging system which would allow the quick, easy and dependable availability of an image reproduction, in both its positive and negative forms, having a quality suitable for use in the graphic arts and other image reproducing applications. As part of the present invention it has been found that by forming a specific layered construction and exposing it through a transparent mask to an U.V. light energy source, the layers may be immediately separated whereby a positive reproduction of the mask image is apparent on one leaf of the separated construction and a negative of said image appears on the other leaf. Furthermore, these images are visible immediately upon exposure and are available after separation for a series of other uses without any further developing treatment. This is an important point of novelty since other prior art systems require some post treatment, such as image curing or development, before a useful product can be attained. One such prior art method requires development by heat treatment, another requires solvent development. Importantly, the present disclosure requires no chemical or other processing subsequent to exposure as is required by such other prior art methods.
Applications for which this dry transfer system is useful include, direct transferability of the image to other surfaces, manufacture of color proofing guides, art composition, engineering drawings, letter and figure transfers, photocomposition, photoresists, nameplates, presensitized printing plates, and bimetal printing plates.
Advantages over the prior art include, the elimination of chemical processing or other treatment to attain the image after exposing; availability of a colored image without subsequent treatments; finer image resolution and a higher degree of energy response since the imaging layer which may be colored is not blended with the energy sensitive layer whereby the functions interfere with one another; no fixing is required; the image is instantly visible upn exposure and may be evaluated for quality without further processing, allowing a continued or multiple exposure if necessary or desirable. Other advantages include safe room light handling; no pollution or exposure of workers to caustic chemicals; and transferable and erasable images in both the positive and negative forms. Importantly, there need not be any alteration of exposures when different colored constructions are selected since the image layer has no effect on the sensitivity of the energy sensitive agent. In systems where both the energy sensitive agent and the imaging agent are blended into one layer the imaging layer absorbs a quantity of the supplied exposure energy and, depending on the amount absorbed by different colorants, the exposure must be adjusted by some factor when changing from one color to another. This adjustment is not required with the instant system.